Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. In general, the wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit (Tx) power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
The OFDMA is a multiple access scheme for allocating subcarriers having orthogonality to respective users. The OFDMA can reduce inter-symbol interference (ISI) and provide a high data rate by supporting characteristics robust to frequency selective fading of a channel. By allocating mutually independent subcarriers to the users, the OFDMA significantly decreases a probability that a specific subcarrier is in a deep fading state with respect to all users. Therefore, since subcarriers have a mutually independent characteristic between users, Tx power decrease and throughput improvement can be achieved by adaptively allocating the subcarriers to a user having a good channel condition.
To overcome performance deterioration caused by channel fading of wireless communication, many researches have been conducted on spatial diversity and/or spatial multiplexing using a multiple input multiple output (MIMO) system. The MIMO system is implemented so that a transmitter and a receiver have two or more antennas, thereby providing advantages such as a high data rate, reliability improvement, channel capacity increase, etc.
Multiple antennas are supported in Institute of electrical and electronics engineers (IEEE) 802.16 (WiMAX) and 3rd generation partnership project (3GPP) long term evolution (LTE) for which standardization has recently been conducted. As disclosed in 3GPP TS 36.211 V8.0.0 (2007-09) “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)”, the 3GPP LTE employs the OFDMA in downlink and employs the SC-FDMA in uplink.
According to the 3GPP TS 36.211 V8.0.0, the 3GPP LTE supports up to 4 antenna ports. However, the number of antenna ports is expected to be greater than that in a next generation wireless communication system requiring a higher maximum data rate. Therefore, there is a need for a method of supporting 4 or more antenna ports in a multiple antenna system.